Yes Exactly, This is not a Valid JSON since they aren't enclosed with double quotes. I manually inserted double quotes and I'm able to parse them using the same logstash configuration. So the only thing missing are the quotes. If i can edit them I'll be able to parse them successfully.
I haven't tried grok for this data since there is already a JSON plugin which does the data parsing with ease. If grok can do it better I'll give it a try. 